purple stems: are from lack of phosphorus i think.
pale color: is either lack of nitrogen or molybdnenum
burnt tips: this is a nitrogen problem cut back on the nutes just a tad and flush with clean water if you use miracle grow STOP. buy a balanced nutrient formula like dyna-grow or something
airflow : keep it above your plants
water: balanced ph is ok but 5.8 to 6.0 is ideal you can get a ph kit from walmart for uber cheap i paid 5 bucks and it has 250 uses just go to either aquariums section or swimming pool section this is a good investment cause low ph can lock out nitrogen which is what happens when you add too much vineagar and high ph is just bad. very very bad. just take 1 gallon of water, test the ph if too acidic add vinegar if too base add lemon juice. add 3 drops then check ph again do this until you get it ideal and count the number of drops this will make it easier on you in the future and if you dont want to you wont have to but another ph kit as long as you dont change water companies.
temperature : 78 degrees (hydroponics water temp 72 degrees)
light : do your research on this you need a hps (sodium) light for flowering keep that in mind
taste : to make it better add sucanat (100% organic dark brown sugar) or sweet ( buy it for 16 bucks from discount-hydro.com)
wilting: mostly caused by either 1. over watering (most likely) or 2 lack of nitrogen
pests : spider mites are a bitch bastard to prevent this have your pot sitting on a "wire table" surrounded by water this brings up humidity tho. and you should watch how the air flows around your plant if it will circulate upwards your good. air from below makes the living conditions for spidermites horrible airflow like this greatly reduces chance of mold also
nutes: self explanatory but add 1tbsp of epsom salts per gallon to your water this will relieve your plant of chemical build ups in the pores on the root hairs thus faster and healthier growth. if you have bad problems post pics we will help